Process for making paper using starch having an increased gel strength

ABSTRACT

Starch is prepared especially for use in the manufacture of paper products by cooking the starch in the presence of aluminum salts at a pH of about 4.0 to 7.0. The treatment is of advantage for lowering the gelatinization temperature of the starch and for increasing the gel strength of the resulting paste. When the treated starch is added to paper pulp it increases the retention of additives and it improves the physical characteristics of the paper product.

United States Patent Hullinger et a1.

1 Feb. 8, 1972 [54] PROCESS FOR MAKING PAPER USING STARCII HAVING ANINCREASED GEL STRENGTH [72] Inventors: Clifford II. Hullinger, Chicago,111.;

Lawrence Cohen, Hammond, 1nd.; Naoyuki Henry Yui, Chicago, Ill.

[52] U.S.Cl ..162/l'75,127/33,127/71, 260/2333 R [51] Int. Cl. ..D2lh3/28 [58] FieldofSearch ..162/175; 260/233.3; 106/210, 106/130; 127/32,33, 71

[56] References Cited UNITED STATES PATENTS 1,907,440 5/1933 Pattillo162/175 2,845,367 7/1958 Alt et al. ..127/32 3,137,592 6/1964 Protzmanet a1. .....127/71 X 3,475,215 10/1969 Maurer ..127/33 X 1,248,03911/1917 Tunnel] ...106/210 X 3,374,115 3/1968 Frank et al ..l27/33 XFOREIGN PATENTS OR APPLICATIONS 145,689 10/1921 Great Britain PrimaryExaminer-S. Leon Bashore Assistant ExaminerFrederick Frei Attorney-Eyre,Mann and Lucas [57] ABSTRACT Starch is prepared especially for use inthe manufacture of paper products by cooking the starch in the presence'of aluminum salts at a pH of about 4.0 to 7.0. The treatment is ofadvantage for lowering the gelatinization temperature of the starch andfor increasing the gel strength of the resulting paste. When the treatedstarch is added to paper pulp it increases the retention of additivesand it improves the physical characteristics of the paper product.

3 Claims, No Drawings PROCESS FOR MAKING PAPER USING STARCII HAVING ANINCREASED GEL STRENGTH In the manufacture of paper and related celluloseproducts, it is of known advantage to add starch to the pulp preferablyat the wet end of the process in order to improve the physicalcharacteristics of the product. Since the starch is not readily retainedby the cellulose fiber, many attempts have been made to improve theretention of the starch and its beneficial effect on the physicalcharacteristics of the product by using starch in a modified form.

It has now been discovered that when starch is cooked at an acid pH inthe presence of an aluminum salt and especially in the pressure of analkali metal aluminate the starch granules swell so much more rapidlythat the gelatinization temperature is reduced and there is a definiteincrease in the gel strength of the paste. Retention of the treatedstarch by cellulose fiber is improved and for some unknown reason theretention of other additives is also improved along with the strength ofthe paper product.

The nature of the mechanism by which the aluminum salts change thecharacteristics of the starch is not known and it may be possible that anew complex molecule is formed. But regardless of the exact mechanismthat may later be proven, it was quite unexpected to discover that thegel strength of the starch actually increased when it was treated at anacid pH in the presence of the aluminum salt. While starch treated inaccordance with the present invention is of particular advantage for usein the manufacture of paper products, it may also be used to advantagein any industrial application where a reduced gelatinization temperatureand a higher gel strength is desirable.

Optimum results are achieved in accordance with the present inventionwhen the starch and aluminum salt are cooked at a pH of about 6.0.Beneficial results may be obtained at a pH of about 4.0 to 7.0. Any ofthe known starches that contain amylopectin such as corn, waxy maize,wheat, potato and tapioca starches may be used in carrying out thepresent invention. If desired the starch may be a British gum or otherstarchy material.

The treatment of starch with the aluminum salt in accordance with thepresent invention must be carried out in the presence of enough waterand at a high enough temperature to cause the granules to swell so thatat least some of the granules rupture and burst open. In general starchgranules will rupture and burst open in the presence of about five ormore parts of water at a temperature of at least about 60 C. The termcooked" and cooking as used in this specification and in the claims isintended to mean that starch is heated in the presence of enough waterto cause starch granules to swell to the point where at least some ofthe granules will rupture and burst open.

The amount of aluminum salt used in treating the starch will varydepending upon the contemplated use of the treated starch. Significantimprovement in the treated starch is realized with as little as 0.1percent by weight of the aluminum salt based on the weight of starch andup to about 30.0 or more percent of aluminum salt may be used. An excessover the amount of aluminum salt that is used in treating the starch maybe of advantage as a convenient way to add aluminum salt per se alongwith the treated starch in certain processes. The aluminum salt employedin treating the starch may be added to the starch granules or topregelatinized starch at any time in any convenient manner as long asthe salt is present when the starch is cooked.

Any of the commercially available aluminum salts which ionize in watermay be used in carrying out the present invention such as aluminumsulfate, aluminum chloride, the alums and other complex salts thatcontain aluminum. Starch treated with the alkali metal aluminates inaccordance with the present invention is of particular advantage for useas an additive to paper pulp. The paper products that contain thesestarches are surprisingly strong and for some unexplained reason thepaper retains a significantly greater amount of additives such astitanium dioxide which is one of the more expensive additives used inthe manufacture of paper that can only be recovered with difficulty fromthe waste water. The alkali metal aluminates that may be used includethe known sodium, potassium, cesium and rubidium aluminates and amongthese the sodium aluminate is preferred since it is inexpensive andreadily available in commercial quantities. Other sodium aluminates thatmay be used are described in US. Pat. No. 2,345,134. In the manufactureof paper as little as 0.2 percent by weight of treated starch based onthe weight of cellulose fiber in the aqueous pulp may be added at thewet end of the process but this amount will vary depending upon processconsiderations and the physical characteristics desired in the product.The treated starch may also be mixed with the dry cellulose fiber. lt ismost convenient however to use a dilute aqueous suspension of thetreated starch containing up to about 5 percent starch solids and addthe suspension to the wet paper pulp before the pulp is embodied in aunitary sheet.

Further details and advantages of the present invention are bestunderstood by reference to the following examples which illustrate someof the embodiments of the invention and scope thereof.

EXAMPLE I In accordance with the present invention, aliquot of ordinarycommercial dent corn starch were cooked in a standard Corn Industriesviscometer with the water bath temperature held at 92 C. and theviscosity of the resulting paste was determined.

The gel strength was also determined in conventional manner using theSaare imbedded disc method in which the force required to pull the discfrom the starch gel gives the strength recorded in grams per squarecentimeter of disc area. In this example the samples were prepared byadding from 0 to L5 percent by weight of commercial sodium aluminatecontaining 23.0 percent by weight of moisture to dent cornstarch andthen each sample was slurried in distilled water to a concentration of5.5 percent by weight of solids.

The sodium aluminate used in the samples was purchased under the tradename of Nalco 680 which is a white powder that contained about 46percent of Al O about 30 percent of Na O in a molecular ratio of Na OIAlO of about l.l5/ l.0. About parts of the powder was soluble in aboutparts of water at 75 F.

As shown in the table below when the normally alkaline pH of the sampleswas adjusted with hydrochloric acid to an acid pH the gelatinizationtemperature (Initial Temperature Rise) was reduced and the gel strengthof the cooked and pasted product was materially increased.

TABLE 1 Initial rise temp, F.

Max. 30 min. vise, g. vista, g.-

cm. cm.

Percent Nalco 680 by weight pH EXAMPLE n An aqueous slurry of commercialcorn starch containing 0.82 percent by weight of aluminum sulfate octadecahydrate (ALlSOtLv l8H O) based on the weight of starch was made upwith 5.5 solids by weight. Aliquots were taken and the pH of each samplewas adjusted with sodium hydroxide. The samples were then cooked and theviscosity and gel strength determined as described in Example I. Theresults were as follows:

TABLE II Max. 30 min. Gel Initial ri e vista. visc., g. strength, plltemp, 1" q.cm. em. sri. em

An aqueous slurry of the same starch cooked in the same manner at thesame concentration in the presence of 0.6 percent by weight of aluminumchloride hexahydrate based on the weight of starch with pH adjusted to6.0 with sodium hydroxide gave an initial temperature rise of 672 C. anda maximum viscosity of 446 g./cm.

The pH of the starch slurry may be adjusted in any convenient manner butchelating acids such as phosphoric or citric acid may tend to decreasethe effectiveness of the material.

EXAMPLE Ill Commercial corn starch containing 0.2 percent sodiumaluminate by weight of the starch granules was slurried in water to aconcentration of 2.0 percent solids. The pH was adjusted to 6.0 withsulfuric acid and the starch was cooked for minutes at 190 F. Theresulting product was added to a conventional paper pulp slurryconsisting of bleached kraft that contained 1 percent rosin and L5percent alum and an ad justed pH of 4.5. The amount of starch added tothe paper pulp slurry was 1 percent by weight based on the weight offiber in the pulp. The addition of the treated starch increased theburst strength of the paper product by 29 percent whereas the additionof the same untreated starch only increased the burst strength by 9percent.

EXAMPLE IV The additives customarily used in the manufacture of paperproducts for retention of starch on cellulose fiber may also be usedwith the treated starch of the present invention. These retentionadditives include materials such as fatty amines, polyacrylamindes,halohydrinamine polymers and polyethylene imine. A conventional solutionof fatty amine sold under the trade name of CAT-5 in an amount of 4.0percent weight of common cornstarch was, added to an aqueous starchslurry containing 5.5 percent by weight of solids. Three aliquots weretaken and cooked as in Example I. The first aliquot contained untreatednatural starch. Sodium carbonate was added to the second aliquot toadjust the pH to 9.0 and 0.02 percent of sodium aluminate (Nalco 680)was added to the third aliquot and the pH was adjusted to 6.0 withsulfuric acid. After cooking each sample was added to a conventionalpaper pulp slurry of bleached kraft that contained 1.0 percent rosin andL5 percent alum and was at a pH of 4.5. In each EXAMPLE V In thisexample the starch retention aid was a polymer of a halohydrin and anamine sold under the trade name of Tylyte 20. An aqueous slurry ofcommercial cornstarch containing 2.0 percent by weight of starch wasprepared by mixing the starch with 0.2 percent by weight of sodiumaluminate (Nalco 680) and 4.0 percent by weight of Tylyte 20 based onthe weight of starch. The sample was divided into three parts. The pH ofPart A was 8.0. The pH of part B was adjusted to 5.0 with aluminumsulfate and the pH of Part C was adjusted to 5.0 with citric acid. Useof the chelating acid decreased the effectiveness of the material asshown below. Each of the three samples were cooked at 190 F. for 15minutes. Two additional samples D and E of commercial cornstarchordinarily used in the manufacture of paper were made and cooked in thesame manner. Sample D was made with a cationic cornstarch and sample Ewith a cationic potato starch.

Each of the samples were added to a conventional paper pulp slurry ofbleached kraft containing 1.5 percent rosin, 1.0 percent alum and 2.0percent TiO The pulp slurry pH was 4.5 and the amount of added starchwas l.0 percent by weight based on the weight of cellulose fiber. Theresulting paper product formed in conventional manner was tested andcompared to a paper blank which did not contain any added starch. Thetest results in the following table were determined by conventionalprocedures employed in the paper pulp industry. The tests used indetermining the values in Table 3 are as follows:

Mullen Burst Strength (also called Burst Factor was calculated from thebursting strength in pounds per square inch (B) used in the formulawhere r is the basis weight in grams per square meter on a moisture-freebasis.

Tensile (also called Breaking Length) was calculated from the formulawherein P is tensile breaking load in pounds on a l5 mm. wide strip, andr is the basis weight in grams per square meter on a moisture-freebasis.

Porosity (also called air-resistance) wherein the values listed are thetimes in seconds required to displace 100 ml. of air through an area of6.45 cm? of the paper.

Tear (also called tear factor) was calculated from the formula wherein eis the force in grams required to tear a single sheet and r is the basisweight in grams per square meter on a moisture-free basis.

Fold (also called MlT folding-endurance) was computed by testing on an,MlT folding tester on strips 15 mm. wide without the exhaust accordingto TAPPI T51 l su-69.

Percent TiO retained was calculated by determining the ash contentaccording to TAPPI T4l3ts-66 by ignition at 925i25 C. in an electricmuffle furnace. There is no loss of volatiles from TiO upon ignition andtherefore the percent TiO retained is obtained from the formula Ashcontent of paper 2.00 (ash content of pulp slurry) X 100 case the amountof added starch was 1.0 percent by weight of the fiber in the pulp. Theimprovement in burst strength of the resulting paper product wasdetermined to be as follows: TABLE 111 Improvement in Bursting MPH: T10S I 5 h l. p )ui's 2 c "r I mduu strength 'lvnslll: lm'oslty 'leitr Foldrutuluml mimic 41.! n, +10 mm ms 1,000 11.4 Starch A. 5r]. 0 7,210 1,am) is. l 1.2m 05. .l 1. Na,( 0, ad usted 1" w 1w.l sun-ch B 55. n 7,200 1,330 is. a 1,220 ml 1.01% NaAlO, adjusted Starch (J. 54. 5 7,165 1,310 46. 6 l, 200 G1. 8 pH 6.0 30.4 Starch 1). 53. (l 7, 020 1, 225 46. 71,170 m. 3 Starch E. 54. 2 7,155 1, 336 46.1 1,215 62.1

Retention of titanium dioxide is extremely desirable in the manufactureof paper. As shown in Table III the starch products of the presentinvention are of material advantage in providing a high level of TiOretention and a surprising increase in the strength of the paperproduct.

It will be understood that it is intended to cover all changes andmodifications of the preferred embodiments of the invention, hereinchosen for the purpose of illustration, which do not constitutedepartures from the spirit and scope of the invention.

What is claimed is:

1. In the process of manufacturing paper products from an aqueoussuspension having cellulosic fiber therein, the improvement whichcomprises the step of adding at least 0.2 percent by weight based on theweight of cellulosic fiber of treated starch to the cellulosic fiber ata point in the process before the aqueous pulp is embodied in a unitarysheet, said starch being treated by cooking it at a pH from about 4.0 to7.0 in the presence of at least 0.1 percent by weight based on theweight of the starch of an aluminum salt which will ionize in water, inorder to cause the starch granules to swell to the point where at leastsome of the granules will rupture and burst and to cause an increase ingel strength of the starch.

2. in the process of manufacturing paper products from an aqueoussuspension having cellulosic fiber therein, the improvement whichcomprises the step of adding at least 0.2 percent by weight based on theweight of cellulosic fiber of treated starch to the cellulosic fiber ata point in the process before the aqueous pulp is embodied in a unitarysheet, said starch being treated by cooking it at an acid adjustedpH-from about 4.0 to 7.0 in the presence of at least 0.1 percent byweight based on the weight of the starch of an alkali metal aluminate,in order to cause the starch granules to swell to the point where atleast some of the granules will rupture and burst and to cause anincrease in gel strength of the starch.

3. In the process of manufacturing paper products from an aqueoussuspension having cellulosic fiber therein, the improvement whichcomprises the step of adding at least 0L2 percent by weight based on theweight of cellulosic fiber of treated starch to the cellulosic fiber ata point in the process before aqueous pulp is embodied in a unitarysheet, said starch being treated by cooking it at a pH from about 4.0 to7.0 in the presence of at least 0.l percent by weight based on theweight of the starch of an aluminum salt which will ionize in water,said cooking being conducted at a temperature from about 60 C. to about92 C. in order to cause the starch granules to swell to the point whereat least some of the granules will rupture and burst and to cause anincrease in gel strength of the starch.

2. In the process of manufacturing paper products from an aqueous suspension having cellulosic fiber therein, the improvement which comprises the step of adding at least 0.2 percent by weight based on the weight of cellulosic fiber of treated starch to the cellulosic fiber at a point in the process before the aqueous pulp is embodied in a unitary sheet, said starch being treated by cooking it at an acid adjusted pH from about 4.0 to 7.0 in the presence of at least 0.1 percent by weight based on the weight of the starch of an alkali metal aluminate, in order to cause the starch granules to swell to the point where at least some of the granules will rupture and burst and to cause an increase in gel strength of the starch.
 3. In the process of manufacturing paper products from an aqueous suspension having cellulosic fiber therein, the improvement which comprises the step of adding at least 0.2 percent by weight based on the weight of cellulosic fiber of treated starch to the cellulosic fiber at a point in the process before the aqueous pulp is embodied in a unitary sheet, said starch being treated by cooking it at a pH from about 4.0 to 7.0 in the presence of at least 0.1 percent by weight based on the weight of the starch of an aluminum salt which will ionize in water, said cooking being conducted at a temperature from about 60* C. to about 92* C. in order to cause the starch granules to swell to the point where at least some of the granules will rupture and burst and to cause an increase in gel strength of the starch. 